1. Field of the Invention
The present invention generally relates to a method for manufacturing semiconductor devices, and more particularly to a method for removing unnecessary oxide layers and particles from the wafer surface and to a method for forming high quality oxide layers on the wafer surface.
2. Description of the Related Arts
In semiconductor fabrication processes, a number of processing steps such as oxidation, etching, lithography, and film deposition are generally required for forming microcircuits on a semiconductor, e.g., a silicon wafer or substrate. During transfer of the wafer after each processing step, the wafer is under exposure to air, and thus the surface of the silicon wafer is covered at all times with a layer of SiO.sub.2, which is gradually thickening with time to an upper limit of about 40 .ANG..
This monolayer of oxide, referred to as native oxide, needs to be eliminated before a subsequent step begins, because the native oxide is an insulating layer which is not designed.
On the other hand, the surface of the silicon wafer is contaminated by such as particles during the transfer. For removing the native oxide and the contaminants from the wafer surface, several techniques have been developed including a wet cleaning method, and a dry cleaning in which either anhydrous HF vapor or H.sub.2 gas is used under high temperature and vacuum conditions. However, the existing cleaning techniques are not satisfactory for removing the native oxide and the contaminants without damaging the wafer surface.
Thin oxide layers such as interlayer dielectrics, gate insulators used in MOS (Metal Oxide Semiconductor) device, and dielectric layers employed in capacitors must represent good insulating property enough to play a role of insulating layers even with very small thickness.
Conventional technique for forming oxide films is carried out in a diffusion furnace in which the silicon wafer is maintained at low pressure and high temperature. The oxide is grown by supplying oxidants, e.g., an oxygen gas into the furnace in atmosphere or nitrogen environment. However, the oxide formed by the conventional technique does not have excellent electrical properties and has a limitation used as an insulating layer.